IEEE 802.16 standard and related international industrial association, such as, WiMAX (Worldwide Interoperability for Microwave Access), work hard to assure that high speed data transmission is available to a large number of users in a large coverage area. In wireless Internet technologies, multicast and broadcast service is provided through MBS zone. FIG. 1 shows an exemplary schematic view of a WiMAX MBS zone architecture. Under this architecture, in an access service network (ASN) environment, after receiving content data from connectivity service network (CSN) 111, a MBS controller 110 transfers the data content stored in a content sync controller server 110a to an anchor 103. Anchor 103 then distributes the content data to other linked sync controllers, such as, a synch controller 113, and a sync executer (SE), such as, SE 121-124. These SEs are distributed in a plurality of MBS zones, such as, MBS zones 101, 102.
Single-BS mode and multiple-BS mode are architectures that may realize MBS zones. In single-BS mode architecture, a mobile station always attaches to a node. In multiple-BS mode architecture, when a mobile station moves from a node to other nodes in the same MBS zone, no handover process is executed. This mobile station may receive the signals from a plurality of nodes in the MBS zone. Under multiple-BS mode architecture, all base stations (BSs) in the same MBS zone need to synchronize.
In the frame-level synchronization technique, when a subscribed service is distributed to a MBS transmission zone, all the MBS zones in the MBS transmission zone need frame-level synchronization. All MBS zones of this MBS transmission zone need to transmit the same content to the subscriber and a MBS controller is responsible for coordination so that all the MBS zones transmit the content in synchronization.
In the macro-diversity level synchronization technique, the physical parameters and the scheduling positions in waveform of all the mobile stations in the same MBS zone need to be identical. FIG. 2 shows an exemplary schematic view of the synchronization architecture. When receiving the content data from a CSN 210, a MBS distribution function unit 220 transfers the content data to a MBS sync controller 230. MBS sync controller 230 generates sync ruler and time information 232 according to the content data and transmits to MBS SE 240. SE 240 uses the information 232 to create the same waveform. Sync ruler is the guideline for creating waveform.
The locations of sync controller and SE depend on the situations. For example, sync controller and upper SE are in the access service network gateway (ASN-GW), while lower SE is in the mobile station. Or, sync controller is in ASN-GW, while SE is in the BS. Or, sync controller is an independent unit and SE is in the BS.
U.S. Pat. No. 6,718,361 disclosed a system for distributing information to a plurality of group members in a communication network. The information distribution system may use unicast to transmit sync message from sync controller to SE. As shown in FIG. 3, an information distribution system 300 includes a content control manager 301 and a group leader, such as, 303a-303c, 305a-305c. Content control manager 301 uses a tree-based structure to unicast sync message to all the connected leaders. The leaders are responsible to transfer the information to other leaders and corresponding clients. In the unicast transmission, sync message is directly transferred to SE instead of through network.
U.S. Pat. No. 6,269,080 discloses a method of using multicast to distribute data file and implement synchronization. As shown in the exemplary flowchart of FIG. 4, a file distribution and synchronization protocol (FDSP) server selects an active receiver from a group of FDSP clients (step 410). The FDSP server multicasts the data file to all the receivers and let the active receiver control the transmission rate (step 420). The active receiver uses unicast to request the FDSP server to retransmit lost data packets (step 430). The FDSP server retransmits lost data packets to respond to the active receiver (step 440). Once the active receiver obtains all the file data, the FDSP server determines whether other FDSP client still needs to obtain data file (step 450). If so, the FDSP server selects a new active receiver from the FDSP clients (step 460). Then, steps 430-460 are repeated until all the FDSP clients receive all the data files transmitted by the FDSP server.
U.S. Pat. No. 6,507,562 disclosed a method for finding an optimal repair tree in multicast communication. The optimal repair tree is formed by a sender station and a plurality of repair head stations. This method finds an optimal repair head station from a plurality of neighboring receivers. The plurality of neighboring receivers dynamically forms a repair group. The repair head station of each repair group is responsible for receiving the ACK and NACK message from the destination station of the repair group, and helps to retransmit the lost data multicast by sender station but not received to the destination station of the repair group.